Lunch Talk (2013)

ASIAA Lunch Talk is an institute-wide event allowing ASIAA researchers from different fields to discuss astronomy in a very casual manner. The informal meeting is usually held at lunch time on every Monday. Occasionally visitors are also invited to the lunch talk to share their research and ideas with ASIAA researchers.

The simple molecular form of oxygen, O2, was thought to be the reservoir of the oxygen budget and the main coolants in the interstellar medium. However, previous searches yielded upper limits on the abundance of molecular oxygen two orders of magnitude below the predictions from gas-phase chemical models. The Herschel Oxygen Project (HOP) is an Open Time Key Project using the HIFI instrument on board the Herschel Space Observatory to carry out a survey with three rotational transitions of O2 toward a broad sample of dense clouds in order to address this important problem in astrochemistry. I will discuss the HOP observations to date, focusing on the detection of O2 toward Orion. With the advantages of the smaller beam and higher sensitivity of HIFI, Goldsmith et al. (2011) reported the first multi-line detections with Herschel toward Orion H2 Peak 1. One possible explanation for the enhanced O2 abundance is thermal desorption of water ice from dust grains, allowing subsequent O2 formation in the gas-phase. Another explanation is that the O2 abundance can be enhanced in mildly shocked gas. I will report new results from observations toward Peak A in Orion, a relatively hot, dense region likely including an embedded protostar ~20" away from H2 Peak 1. By comparing the line intensities toward the two observed positions, I will discuss the implications of the source of emission and oxygen chemistry

2

2013-12-23 Mon12:00~13:00R1203

Hung-Yi Pu[ASIAA]

Black hole shadow

Abstract

One of the major goals of the VLBI/GLT (Greenland Telescope Project) in ASIAA is to observe the "shadow" of the supermassive (~6 billion solar masses) black hole at the center of M87 with super-high (~micro arcsec) resolution. Such shadow is expected to be observed when a black hole is surrounded by a bright source, such as an accretion disk or jet. In this talk, I will introduce how to model a black hole shadow image and explain some interesting shadow features resulting from the spin of the black hole.

3

2013-12-16 Mon12:00~13:00R1203

Meg Schwamb[ASIAA]

Planet Hunters: Searching for Exoplanets with 500,000 Eyes

Abstract

NASA's Kepler spacecraft has spent the past 4 years monitoring over ~160,000 stars for the drop in light due to a transiting exoplanet. Planet Hunters (http://www.planethunters.org), part of the Zooniverse's (http://www.zooniverse.org) collection of online citizen science projects, uses the World Wide Web to enlist the general public to identify transits in the pubic Kepler light curves. Planet Hunters utilizes human pattern recognition to identify planet transits that may be missed by automated detection algorithms looking for periodic events. Referred to as ‘crowdsourcing’ or ‘citizen science’, the combined assessment of many non-expert human classifiers with minimal training can often equal or best that of a trained expert and in many cases outperform the best machine-learning algorithm. Visitors to the Planet Hunters' website are presented with a randomly selected ~30-day light curve segment from one of Kepler’s ~160,000 target stars and are asked to draw boxes to mark the locations of visible transits in the web interface. 5-10 classifiers review each 30-day light curve segment. Since December 2010, more than 260,000 volunteers world wide have participated, contributing over 20 million classifications. We have demonstrated the success of a citizen science approach with the project’s more than 20 planet candidates, the discovery of PH1b, a transiting circumbinary planet in a quadruple star system, and the discovery of PH2-b, a confirmed Jupiter-sized planet in the habitable zone of a Sun-like star. I will provide an overview of Planet Hunters, highlighting several of project's most recent results and discoveries.

4

2013-12-02 Mon12:00~13:00R1203

Yao-Yuan Mao[Stanford U.]

Dark Matter in the Milky Way

Abstract

We use zoom-in simulations to study the properties of dark matter
halos the local distribution of dark matter. One particular
application is to find a cosmologically motivated model for the
Galactic velocity distribution function (VDF) of dark matter, which is
one of the most important astrophysical uncertainties in direct
detection experiments. We propose a new VDF model, test it against
simulated halos with a wide range of properties, and demonstrate that
direct detection results could be interpreted very differently,
especially in the low-mass WIMP regime. In addition to this
application, I will also talk about our ongoing work on a suite of
zoom-in simulations of Milky Way size halos.

We report the stellar mass fraction, cold baryon fraction, gas mass fraction and the total baryon fraction for 14 massive clusters detected by Sunyaev-Zel’dovich effect (SZE) by South Pole Telescope (SPT) at redshift from 0.576 to 1.32. This work provides the highest redshift sample up-to-date to study the evolution of stellar and gas components in the galaxy clusters with a wide range of redshift and the median mass ( M500 ) of 9×1014 M⊙ . We measure the stellar masses for both the full cluster galaxy and the passively evolving galaxy populations of 14 clsuters using the broadband photometry information from B band to near-infrared. The gas mass is estimated from CHANDRA and XMM- Newton X-ray observations while the total mass M500 is derived and well-calibrated from SPT observable. We find the decreasing stellar mass fraction and the cold baryon fraction, but the oppositely increasing the gas fraction and the total baryon fraction, in the more massive clusters for our SZE-selected clusters in the high redshift, which is in a good agreement with the previous studies with the samples which are selected by X-ray and/or optical surveys in the local Universe (z < 0.1). We do not see the clear redshift evolution for stellar mass fraction, cold baryon fraction, gas mass fraction and the total baryon fraction in our sample and combining the results of local Universe from the literature, suggesting that the baryon contents in the clusters have been established in the very early Universe and are dominated by the gravitational potential. We estimate the mass fraction of the passively evolving galaxy population (red fraction) for 14 clusters in this work. The individual red fraction of the cluster is suffering from the noisy background subtraction while the average red fraction among our sample is about 70.7 ± 8.4 %, implying that the cluster galaxy population is mainly dominated by the passively evolving galaxy population. Our work significantly probes the formation history from the previous studies of local Universe to the high redshift

6

2013-11-04 Mon12:00~13:00R1203

Geoff Bower[UC Berkeley]

Galactic Center Pulsar, SGR J1745-29

7

2013-10-28 Mon12:00~13:00R1203

Ryan Keenan[ASIAA]

The weather in Shanghai: A Rising Storm of Chinese Astronomy

8

2013-10-07 Mon12:00~13:00R1203

Hsi-An Pan[NAOJ]

Gas and Star Formation Properties in Barred Spiral Galaxies: from global to local

9

2013-09-30 Mon12:00~13:00R1203

Yiming Li[U of Mass]

A Golden Standard of Star Formation Rates

10

2013-09-16 Mon12:00~13:00R1203

Ramon Brasser[ASIAA]

Online privacy and anonymity in the surveillance era

Abstract

In June whistleblower Edward J. Snowden revealed to the world that several government agencies in the west were engaging in the collection of bulk internet data from people all over the world. This revelation probably consists of the greatest online privacy violation ever seen. In this lunch talk I will discuss several measures that can be taken to improve your online anonymity and make it more difficult for the government or large corporations to track and monitor your behaviour.

11

2013-09-09 Mon12:00~13:00R1203

Mubdi Rahman[JHU]

From Clusters to Associations: The Evolving View of Star Formation

Abstract

Our picture of star formation has long been biased towards compact clusters, those being the easiest to observe and characterize. However, theoretical and observational work over the past decade has begun to show that the compact cluster view of star formation is more of an exception, and the standard model looks more like a quickly dissipating association, with important consequences for feedback and galactic archaeology. In this talk, I'll discuss the growing evidence for this new model, some of its consequences, and what the next steps are to create a more accurate global picture of star formation.

12

2013-09-02 Mon12:00~13:00R1203

Bernd Liebig[ASIAA]

An introduction to experimental plasma physics

13

2013-08-26 Mon12:00~13:00R1203

Patrice Theule[Aix-Marseille University]

Current challenges on gas-grain astrochemical models

Abstract

Gas-grain models are used by astronomers to interpret observations of molecular abundances in different objects. In this talk I will review the basic principles of gas-grain astrochemical models. Over the years grain chemistry appeared to play a significant role in interstellar chemistry. However, solid-state chemistry is currently poorly known and still a challenge. I will also focus on several issues related to the solid-state part of the astrochemical models,and on the ways to improve them.

14

2013-08-19 Mon12:00~13:00R1203

Ming-Chang Liu[ASIAA]

The final report of the NanoSIMS project, and where are we going with this instrument?

15

2013-08-12 Mon12:00~13:00R1203

Ryan Keenan[ASIAA]

Update from the 'Ripples in the Cosmos' meeting held in Durham, England July 22-26, 2013

16

2013-07-22 Mon12:00~13:00R1203

Hsian-Hong Chang[ASIAA]

Recent results of HEB development

17

2013-07-15 Mon12:00~13:00R1203

Chau-Ching Chiong and Hiroyuki Hirashita[ASIAA]

SKA Science Workshop in East Asia 2013

18

2013-07-08 Mon12:00~13:00R1203

Liang-Yao Wang[ASIAA]

Molecular Jet of IRAS 04166+2706

Abstract

In this lunch talk I will introduce our observational results of the molecular outflow from the Class 0 protostar IRAS 04166+2706. The central arc-minute of the molecular jet is mapped with the Submillimeter Array (SMA) in CO J = 3–2 at an angular resolution of ~1 arcsec. On the channel map, conical structures are clearly present in the low velocity range (|V−V0| <10 km s−1), and the highly collimated knots appear in the Extremely High Velocity range (EHV, 50> |V−V0| >30 km s−1). The field of view covers the inner four pairs of the symmetric knots, and both the innermost knots R1 and B1 in the red- and blue-shifted lobes have the highest velocities within the sequences. Although the general features appear to be similar to previous CO J = 2–1 images in Santiago-Garcia et al. (2009), emission in CO J = 3–2 almost always peaks further away from the central source than that of CO J = 2–1 in the channel maps. I will present and discuss the results in this talk.

19

2013-07-01 Mon12:00~13:00R1203

Ramon Brasser[ASIAA]

Long-term climatic stability on exoplanets

Abstract

One of the major goals of planetary science is to determine whether or
not Earth is unique as a habitable planet. With the recent surge in
planetary discoveries from the Kepler mission and from RV surveys such
as HARPS we know of approximately 160 planets in the habitable zones of
other stars. Thus a detailed investigation of their habitability is
warranted.
Here we determine a planet's habitability from a dynamical point of
view, focusing on the coupling between the orbital forcing of
eccentricity and obliquity and how this affects the insolation at summer
solstice. On Earth the insolation at the high latitudes during summer
solstice is known the drive the ice ages, whose forcing is driven by
obliquity and precession cycles. By studying similar cycles on
exiplanets we can determine whether such planets undergo regular ice
ages, and their magnitude, or whether there exist any planets whose
long-term climatic cycles are as stable as those of the Earth.
We present the results of the climate cycles on the super Earth HD 40307
g. We first determine the dynamical stability of the whole system using
numerical simulations. Once a stable solution is obtained we simulate
the obliquity and precession response of planet g caused by the forcing
of the other planets assuming a range of initial obliquities and
rotation periods. The results are then used to determine the insolation
at summer solstice, from which we compute the long-term trend in global
temperature.
This is a work in progress and I will finish this presentation by
discussing the future of this project and the large amount of work that
needs to be done. It requires multidisciplinary collaborations with
atmospheric scientists, geophysicists and astrobiologists.

20

2013-06-24 Mon12:00~13:00R1203

Sung-Nien Hsieh[ASIAA]

A brief introduction to Spectrum Analyzer

21

2013-06-17 Mon12:00~13:00R1203

Chin-Fei Lee[ASIAA]

What happened to the Pre-Planetary Nebula (PPN) CRL 618 in the last 100 yrs

22

2013-06-03 Mon12:00~13:00R1203

Ya-Lin Wu[U of Arizona]

Magellan AO System and Its First Light Results

Abstract

Magellan AO system (MagAO) is a new adaptive optics system used with the 6.5 m Clay Telescope. Utilizing a 585-acturator adaptive secondary mirror to correct phase distortions, MagAO is the world’s first AO system which demonstrates reasonable performance in visible wavelengths, with Strehl ratio ~30% and resolution ~20 mas. Various science targets, including protoplanetary disk, binary star, and exoplanet, were imaged during the first commissioning run. I will talk about the first light results in this 20-minute presentation.

23

2013-05-20 Mon12:00~13:00R1203

Yasuhiro Hasegawa[ASIAA]

The statistical properties of planets formed at multiple planet traps: the predominance of gas giants around 1 AU and super-Earths

24

2013-05-13 Mon12:00~13:00R1203

Jiyeon Seok[ASIAA]

Formation History of Polycyclic Aromatic Hydrocarbons in Galaxies

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are one of the major dust components in the interstellar medium (ISM). We present our evolution models for the abundance of PAHs in the ISM on a galaxy-evolution timescale. We consider shattering of carbona- ceous dust grains as the formation mechanism of PAHs while PAHs can be reduced by coagulation onto dust grains, destruction by supernova shocks, or injection into star formation. We implement these processes in a one-zone chemical evolution model to obtain the evolution of the PAH abundance in a galaxy. We find that while the de- struction by supernova shocks is the primary destruction mechanism in the metal-poor environment, the coagulation governs the destruction of PAHs in the metal-rich envi- ronment. We compare the calculated PAH abundances with the observed abundances in galaxies of various types. We discuss the physical properties that play a key role in the evolution of PAH abundance.

25

2013-05-06 Mon12:00~13:00R1203

Sundar Srinivasan[ASIAA]

The Evolved-Star Dust Budget in Nearby Galaxies

Abstract

Evolved objects such as red supergiants (RSGs) and asymptotic giant branch (AGB) stars inject metal-rich material in the form of gas molecules and solid dust particles into the interstellar medium (ISM) of their host galaxies, where they may seed and be incorporated into the next generation of stars. This mass loss from AGB and RSG stars thus drives galactic chemical evolution, and the total dust production rate from these stars is an important parameter that can be used to constrain evolutionary models.
In order to quickly compute the total dust budget for large photometric datasets, we have constructed a Grid of RSG and AGB ModelS (GRAMS, Sargent et al. 2011, Srinivasan et al. 2011) for the dusty shells around these stars. The models, when fit to the observed data, provide reliable estimates of the luminosities and dust production rates (DPRs). We have already used our models to study the AGB/RSG population in the Magellanic Clouds (Riebel et al. 2012, Srinivasan et al. in prep), for which we had photometry and spectra as part of the SAGE (Surveying the Agents of Galaxy Evolution, Meixner et al. 2016), SAGE-SMC (Gordon et al. 2011) and SAGE-Spec (Kemper et al. 2010) programs, and we are now extending our work to other galaxies in our neighbourhood.
In this talk, I will describe our model grid and present our results for the Magellanic Clouds as well as for the galaxy M33. Our method provides a quick way of estimating the dust budget for entire galaxies, which will allow us to probe the dependence of this mass loss on properties of the host galaxies.

26

2013-04-29 Mon12:00~13:00R1203

Yun-Hsin Huang[ASIAA]

Constraining the mass-richness relation of galaxy clusters using large scale clustering

The Subaru prime focus spectrograph (PFS) is a multi-fiber spectrograph that can provide an field of view (FOV) of 1.3 deg on the sky, covering optical to part of NIR wavebands (0.38 - 1.26 microns) with 2400 fibers and an averaging spectral resolving power of ~3000. Compared with other optical multi-fiber spectrographs, PFS offers a combination of large FOV and large number of fibers on a 8-m class telescope. Science targets of PFS are cosmology, Galactic archaeology and galaxy/AGN evolution. PFS is composed of four main components: prime focus instrument (PFI), fiber connector/cables, spectrographs and the metrology camera system. ASIAA is in charge of part of PFI and the entire metrology camera system. I will briefly introduce the metrology camera system, including its requirements, optical design and the progresses we have made so far

28

2013-04-15 Mon12:00~13:00R1203

Zhi-Wei Zhang[ASIAA]

Current status of the TAOS project

29

2013-04-01 Mon12:00~13:00R1203

Hsiang-Hsu Wang[ASIAA]

Formation and Dynamical Effects of Circumplanetary Disks

Abstract

A circumplanetary disk (CPD) may play a key role in the process of planet formation in many aspects, for instance, the gas accretion rate, formation of satellites as well as the long-term averaged torque exerting on protoplanets. We performed 2D and 3D global simulations to study the properties of CPDs that are embedded in an isothermal viscous protoplanetary disk. Without introducing a softening length to the protoplanetary potential, the structure and the gas dynamics of CPDs are properly resolved by using the technique of nested mesh refinement. Our 3D isothermal calculations show that prominent CPDs can form around low-mass protoplanets. Since these CPDs are constantly disturbed by the surroundings, CPD+protoplanet is not an isolated system as usually assumed in the literature for planet migration. The asymmetry of the CPD with respect to protoplanets may have significant impact on planet migration, especially for the low-mass protoplanets. In this series of work, detailed study on the properties of CPDs is first explored with 2D calculations. The dynamical role of CPDs as well as the effects of viscosity are systematically investigated. From our 2D results, we conclude that torques from CPDs exerting on protoplanets are significant compared to that outside of the Hill radii. The effect of viscosity is to reduce the mass accretion rate onto CPDs in the high-mass models.

30

2013-03-18 Mon12:00~13:00R1203

I-Ting Ho[University of Hawaii]

Illustrations of dissecting galaxies - in the context of chemical evolution

31

2013-03-11 Mon12:10~13:10R1203

Jen-Chieh Shiao[Inst. of Oceanography, NTU]

Biological and environmental information recorded in fish otolith

Abstract

Otoliths, which are calcium carbonate structures in the inner ears of teleostean fish, function as balance and auditory organs. The acellular and metabolically inert otoliths grow continuously throughout the life of a fish and record the biological events and environmental characteristics e.g., temperature and salinity experienced by the fish. Examination of otolith microstructure and chemical compositions have extensive applications, such as for biologists to reveal life history events of the fishes as well as for geologists to reconstruct paleoclimate

32

2013-03-04 Mon12:00~13:00R1203

Hau-Yu Liu[ASIAA]

Imaging the Molecular ISM in the Galactic Center

33

2013-02-25 Mon12:00~13:00R1203

Ya-Wen Tang[ASIAA]

The circumstellar disk of AB Aurigae: evidence for envelope accretion at late stages of star formation?

34

2013-02-18 Mon12:00~13:00R1203

Yu-Yen Chang[MPIA]

How did the Largest Ellipticals Form?
--Structural Evolution of Galaxies in CANDELS